1. Field of Invention
The present invention generally relates to bolus-chasing angiography wherein imaging data is analyzed more effectively, tolerating greater modeling errors and uncertainties, using more powerful and robust control techniques and incorporating faster and more robust identification/estimation algorithms and techniques.
2. Description of Prior Art
As known in the prior art, administration of a contrast material or bolus provides a short temporal window for optimally imaging the vasculature, lesions and tumors. Optimization of contrast enhancement becomes increasingly crucial with the wide use of CT and Magnetic Resonant Image (“MRI”) technology, given the dramatically shortened image acquisition time. Recently, CT began a transition into sub-second scanning, cone-beam geometry and real-time imaging with the introduction of multi-slice/cone-beam systems.
A number of clinical studies were reported on contrast enhancement for CT in the past. However, the existing results on modeling of CT contrast bolus dynamics are very limited.
To obtain the highest image quality in CT angiography at the lowest dosage of contrast material, strategies for bolus administration and CT data acquisition must be individualized and optimized. It is desirable to scan when the intravascular concentration of contrast material is at its peak.
Scanning too early may result in over-estimation of stenosis, while scanning too late may result in overlap of venous structures.
Three methods have been developed to individualize scan timing:                (1) test-bolus timing,        (2) region of interest (ROI) threshold triggering, and        (3) visual cue triggering.        
For the test-bolus method, there is a risk of decreasing target lesion conspicuity due to equilibration of the test-bolus. For the two triggering methods, they are vulnerable to patient motion, usually related to breathing, which may displace the target organ or vessel from the scan plane.
Moreover, one of the fundamental limitations with all the three methods is that they provide little data for matching the table/gantry translation to the contrast bolus propagation. Bolus dynamics is complicated by multiple interacting factors involving the contrast administration protocol, imaging techniques, and patient characteristics. In particular, the current patient table is translated at a pre-specified constant speed during data acquisition, which cannot be altered adaptively to chase the contrast bolus for optimally enhanced CT images.
With a pre-set scanning speed, it is difficult and often impossible to synchronize the central scanning plane with the longitudinal bolus position. This misalignment becomes more problematic to image quality when spiral scanning speed is fast (with multi-slice spiral CT), contrast volume is small and/or injection rate is high (leading to reduced peak duration), as well as when there are large or small capacity vessels, either from aneurysm formation or occlusive disease.
U.S. Pat. No. 6,535,821 (Wang et al.) (the '821 patent), which is incorporated herein in its entirety by reference thereto, discloses a system and method for optimization of contrast enhancement utilizing a bolus propagation model, a computerized predictor of the bolus position, and a real-time tomographic imaging system with an adaptive mechanism to move a patient and/or the imaging components (either the entire gantry or its essential parts).
In the '821 patent, a monitoring means for measuring the position of a bolus moving along a path in a biological structure is provided. A predicted position of the bolus is determined using a bolus propagation model with a set of parameters. The predicted position of the bolus is compared with the measured position of the bolus. A filtering means is provided for reconciling a discrepancy, if any, between the predicted position of the bolus and the measured position of the bolus, to derive a set of control parameters. Finally, a control means is provided for receiving the set of control parameters, to adaptively transport the table to chase the moving bolus.
While the system and method disclosed in the '821 patent represents a major improvement over prior systems and methods, there is a need for making the implementation of bolus chasing imaging in practice efficient and possible by reconstructing and analyzing imaging data in more effective ways, tolerating greater modeling errors and uncertainties, using more powerful and robust control techniques, and incorporating faster and more robust identification/estimation algorithms and techniques.